Figure 2. Anatomical characterization of GF guidance defects of mutant L1CAM protein expressions in nrg⁸⁴⁹ background.

(A) Schematic of the giant fiber (GF) to TTM (Tergo-trochanteral Muscle) circuit in Drosophila. The GF soma in the brain extends an axon into the second neuromere of the VNC, where it synapses with the Tergo-trochanteral motor neuron (TTMn), which itself innervates the TTM. Rectangle highlights the brain region depicted in B-F. (B) GF anatomy in the brain of a wild-type control fly. Scale bar represents 50 µm. (C) In a nrg⁸⁴⁹ animal two GFs were seen to stall in the suboesophageal ganglion. (D) Expression of wild-type human L1CAM in the GF in the nrg⁸⁴⁹ background rescued the axonal guidance defect. Expression of L1-Y1070C (E) or L1-H210Q (F) in the nrg⁸⁴⁹ background did not rescue or only partially rescued the axonal guidance phenotype. (G) Bar graph shows the quantification of the axonal guidance defects. The rescue of the nrg⁸⁴⁹ guidance phenotype by expression of UAS-nrg¹⁸⁰, UAS-L1 and the various mutant L1-constructs represented in percent values. The significant differences (Chi-square analysis, p≤0.05) between Nrg¹⁸⁰, L1, L1-L120V and L1-E309K expression in the nrg⁸⁴⁹ background and negative control flies (nrg⁸⁴⁹) are indicated by asterisks.